Police said that they were called at 7.05am to reports that a man had fallen from a building in Kilburn High Road.
Officers attended the scene along with paramedics from the London Ambulance Service.
The man was rushed to hospital, where he remains in a life-threatening condition.
Kilburn High Road near the Overground station was closed for more than an hour this morning while emergency services worked at the scene.
Police said that enquiries to establish the circumstances are ongoing.
If you feel affected by what has happened and wish to find support, you can contact the Samaritans on 116 123 via phone for a confidential chat or email jo@samaritans.org
